Periscopic bore sight



June 17, 1947.

L. H. BROWN 'PERISCOPIC BORE SIGHT Filed Dec. 15, 1945- I LEu-H EruwT'LPatented June 17, 1947 UNITED STATES PATENT OFFICE PERISCOPIC BORE SIGHTLeo H. Brown, Glenville, Conn.

Application December 15, 1943, Serial No. 514,356

13 Claims. (01. 8874) (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described hereinmay be manufactured and used by or for the Government for governmentalpurposes without the payment to me of any royalty therein.

The invention pertains to a novel apparatus for bore sighting a gun. Theoperation consist generally in truing the external sighting device onthe gun with respect to the axis of the gun barrel by directing bothtowards a distant object such as a star. In this operation it isessential that the object be sighted accurately in the center of the gunmuzzle.

This invention has for its object a simple device for satisfying thestated requirement. Another object is to provide a device that does notrequire the operator to apply the usual cross-wires over the muzzle ofthe gun from without, and thereby expose himself to enemy fire.

The device of the invention comprises, in general, a disk or frame to beinserted in the chamber of the gun and having a central aperture throughwhich the distant object is sighted directly. For the purpose ofdetermining that the object is centered in the muzzle, the frame carriesone or more periscopic systems, preferably radially disposed, to producea View or views of the object at the point of observation. Each of theseviews includes a segment of the periphery of the muzzle of the bore; andwhen the object or a portion thereof is centered on the said segment, itfollows that the object is centered in the muzzle. Greater accuracy isobtained by providing a plurality of such periscopic systems,advantageously at least three, and whose objective reflectors arearranged on a circle to approximate that represented by the periphery ofthe bore of the gun barrel.

An illustrative embodiment of the invention is disclosed in thefollowing description and in the accompanying drawings in which:

Figure 1 is a longitudinal section of a gun barrel with the device ofthe invention mounted therein;

Figure 2 is an elevation of the device;

Figure 3 is a section on the line 33 of Figure 2, and

Figure 4 is an illustration of the composite image seen by the observer.

Figure 5 is a detail showing a modification.

In Figure 1 is shown a gun barrel 1 having at its forward end the usualmuzzle 2 and at its rear end the usual chamber 3. The bore sightconstituting this invention includes a frame or disk 4 adapted to befitted in the chamber 3, across the axis thereof, and having a centralaperture 5 centered on the axis. The distant reference object used forsighting is visible directly through the aperture 5 by the observerwhose eye 6 is positioned at a suitable distance behind the aperture. Bythis means alone, the distant object can be centered only approximatelyon the axis of the gun barrel.

The accuracy of the centering is improved and substantially perfected byan optical system for forming at least one and. preferably a pluralityof views of segments of the muzzle end of the bore and of the object ora common part thereof around the aperture 5 in a position to be viewedby the observer at location 6. This optical system, in the embodiment ofthe invention illustrated, consists of a plurality of periscopes mountedradially in the disk 4 between its periphery and the aperture 5. Foreach periscope, the disk is formed with a radial slot 1 having mirrors 8and 9 disposed respectively at the outer and inner ends thereof. It willbe understood, however, that prisms may be employed in lieu of mirrors.

Each outer mirror 8 is so positioned as to pick up rays of lighttraveling along the inner wall ID of the gun barrel I. Some of theserays will obviously be received from the distant object on which the gunis sighted. The inner mirrors 9 receive light from the mirrors 8 and arepositioned to reflect this light to the observation point 6 as indicatedby the rays II in Figure 1.

Through the aperture 5 the observer sees the rifled inner wall of thegun barrel as illustrated in Figure 4. He also sees the distant objectI2 on which the gun is sighted. Each of the periscopes gives a view of aportion IU of the wall l0 and a view l2 of the object l2. When each viewl2 of the object is in the same spatial relation to the correspondingview of wall portion Hi, the line of sight on the object is coincidentwith the axis of the bore of the gun barrel. This condition signifiesaccurate sighting of the gun on the distant object. If it is assumedthat the distance of the object is infinite, each view 12' of the objectI 2 will lie adjacent the are defined by the periphery of the muzzle 2in each view of a portion ll) of the gun bore.

In Figure 5 is shown a modification wherein prisms I3 are employed inplace of the mirrors 8 and 9. This type offers several advantages ofassembly and maintenance. For instance, it is much easier to grind theend faces of a prism to the proper angles than it is to mount smallmirrors at the proper angles, and in the case of mirrors, contact isdifficult for cleaning, whereas in the case of a prism only two surfacesneed be cleaned and these are easily contacted.

While preferably three or four pairs of reflectors are employed, equallyspaced about the bore of the gun, fairly accurate results may beobtained by the use of a single pair of reflectors. This is because,when sighting upon an object such as a star that may, for all practicalpurposes, be assumed to be at an infinite distance, the object willappear to coincide with the muzzle edge of the bore and to be centeredwith respect to the image of the arc of said edge, when the gun isproperly bore sighted. Therefore, if the image is centered withinaperture 5 as closely as possible, and is also positioned with respectto one image of the muzzle edge as shown in Figure 4, the gun is boresighted with a fair degree of accuracy.

By means of the apparatus herein described, the bore sighting operationmay be performed from within the protective enclosure. The operator isnot required to expose himself to enemy fire by going to the muzzle ofthe gun for mounting the cross wires in the conventional manner. Thischaracteristic of the invention is especially valuable in tank warfare.

While a specific embodiment of the invention has been shown and beendescribed, it will be understood that various alterations may be madewithout departure from the spirit of the invention as indicated by theappended claims.

What I claim is:

1. In combination with a gun barrel, a frame mounted at the breech endof said barrel and having a sighting aperture centered on the axis ofthe bore of said barrel, a plurality of first reflecting means carriedby said frame and positioned to reflect respective images ofcircumferentially spaced portions of the muzzle end of said bore andrespective images of a distant object, and second reflecting meansdisposed radially inwardly of said first reflecting means and positionedto reflect said images rearwardly adjacent and along said axis to anobservation point on said axis at the breech end of said bore wherebythe images of a distant object may be observed in relation to the imagesof said portions, simultaneously with direct observation of said objectthrough said aperture.

2. In a bore sighting device, first means adapted to be positionedacross and in predetermined relation with the breech portion of a gunbore, said means defining a plurality of angularlyrelated planes eachcontaining the axis of said bore, and light-reflecting means carried bysaid first means to project respective images of each portion of thebore at the muzzle intersected by said planes together with images of aremote object, radially inwardly, then rearwardly closely adjacent andalong said axis, whereby an observer at the breech may simultaneouslyobserve said images.

3. A bore sighting device comprising a disc having a central apertureand slots extending radially of said aperture to define radial planescontaining the axis of a gun bore when said disc is positioned centrallyof and across a breech portion of the bore of a gun, and a pair ofmirrors mounted in and adjacent opposite ends of each slot,respectively, each pair of mirrors being ositioned to project an imageof one of the muzzle portions of said bore intersected by the plane ofits slot, together with an image of a remote object, radially inwardly,then rearwardly adjacent and along said axis, whereby an observer atsaid breech portion may simultaneously observe a distant object throughsaid aperture and a plurality of images thereof with relation to therespective images of said muzzle portions.

4. A bore sighting device comprising a disc having a central viewingaperture, said disc being adapted to be positioned across a breechportion of the bore of a gun with said aperture on the axis of saidbore, there being a plurality of slots in said disc extending radiallyfrom said aperture to define respective radial planes with said boreaxis, and reflector means mounted within each said slot and carried bysaid disc to deflect light rays passing along the respectiveintersections of said planes with said bore surface, radially inwardlythen rearwardly from said disc along and closely adjacent the axis ofsaid bore to a common point of view, the light rays deflected by eachsaid reflector means including an image of the muzzle portion of saidbore intersected by its plane; together with an image of a remote targetwhen said bore axis is aligned with said target.

5. In a bore sighting device, a disc adapted to be secured inpredetermined position across the breech portion of the bore of a gun,there being slots in said disc extending radially of the bore axis anddefining with said axis, radial planes, and a plurality oflight-reflecting means carried by said disc each being positioned withina respective slot to project a discrete image of the muzzle portion ofsaid bore intersected by the respective one of said planes together withan image of a remote object when aligned with said bore axis, radiallyinwardly of said disc, then rearwardly along the axis of said bore to apoint on said axis adjacent the breech of said gun.

6. In combination with a gun barrel, first means defining a plurality ofradial planes containing the axis of the bore of said barrel, and lightreflecting means carried by said first means and adapted to projectimages of the muzzle portions of said bore intersected by said planes,and images of a remote target when in alignment with said axis, radiallyinwardly, then rearwardly adjacent and along said axis to a viewingposition rearwardly of said bore.

'7. In a bore sighting device, means adapted to be secured across abreech portion of the bore of a gun and carrying means to define aplurality of angularly-related planes each containing the longitudinalaxis of said bore, said last-named means including a first reflectoradjacent and at 45 to each respective line of interesection of a saidplane with the surface of said bore, and a second reflector parallel toand radially inward of each corresponding first reflector, wherebydiscrete images of the muzzle portions of said bore intersected by saidplane respectively together with images of a remote object in alignmentwith said axis, are projected rearwardly along said bore axis to anobservation point.

8. In a bore sighting instrument, a disc having a sighting aperturecentrally thereof and angularly-spaced slots extending radially of saidaperture, said disc being adapted to fit within and across the breechportion of a gun bore so that the aperture lies on the axis of said boreand the radial slots in said disc define with said axis, angularlyrelated planes intersecting said bore along elements thereof, a mirrorin the radially outward end of each slot and positioned adjacent and at45 to its respective element, a

Search second mirror in the radially inward end of each slot parallel toits respective first mirror, whereby each pair of mirrors projects animage of a distant object in alignment with said axis and an image of amuzzle portion of said bore intersected by the corresponding plane, forobservation simultaneously with direct observation of said objectthrough said aperture.

9. In a bore sighting device, a disc having a central sighting apertureand angularly-related slots extending radially of said aperture, saiddisc being adapted to fit within and across the breech portion of thebore of a gun so that the aperture therein lies on the axis of saidbore, and an optical reflectin element positioned within each said sloteach element acting to project an image of a portion of the boreadjacent the muzzle, together with an image of a distant object whensaid axis is aligned therewith, radially inwardly along its slot, thenrearwardly along and adjacent said axis, whereby a plurality of imagesof said distant object and images of said portions, may be viewedsimultaneously with observation of the object itself through saidaperture.

10. In a bore sighting device, a frame having a central sightingaperture and adapted to be secured across the breech portion of the boreof a gun, means carried by said frame for engaging the gun bore atcircumferentially-spaced points to thereby positively locate saidaperture on the longitudinal axis of said bore, and optical meanscarried by said frame to project an image of a sector of the muzzleportion of said bore and an image of a distant target when aligned withsaid axis, first radially inwardly, then rearwardly along and closelyadjacent said line of sight whereby said target and an image thereof inrelation to said muzzle portion, may be simultaneously observed thedirect view of said target and its image being discrete.

11. In combination with a gun barrel, four substantially equally spacedlight reflecting means positioned at the breech of the barrel, saidmeans being disposed adjacent the surface of the bore of the barrel andinclined so as to reflect radially inwardly four discrete images ofrespective circumferentially-spaced segments of the muzzle of the gunand four images of a distant object, and other light reflecting meanslight reflecting means and positioned so that the four separate imagesof said respective segments and the four images of the object reflectedby said first named reflecting means, are reflected thereby into theeyeof an observer positioned at the rear of the gun barrel.

12. In combination with a gun barrel, a plurality of plane lightreflecting surfaces, spaced circumferentially of the gun bore adjacentthe wall thereof and inclined to the axis of said bore so that each saidsurface projects radially inwardly of said bore and image of a segmentof the muzzle of said gun including the image of a remote object whenaligned with said axis, said segments being circumferentially spaced,and a number of light reflecting means equal to said light reflectingsurfaces, each said means being positioned radially inwardly of acorresponding surface and inclined to the bore of said gun, to projectrearwardly along the axis of said bore to the eye of an observerdiscrete images of a respective segment and said object.

13. In a bore-sightin device, a disc having a central sighting aperturetherein and adapted to be secured within the breech end of a gun borewith said aperture positioned upon the longitudinal axis of said bore,means carried by said disc and defining, with said axis, a planeextending radially of said axis and intersecting the surface of saidbore along an element thereof, and optical means on said disc to receiveand project an image of a limited muzzle portion of said boreencompassing said element, together with an image of a distant objectwhen aligned with said axis, first radially inwardly of said disc, thenrearwardly along and closely adjacent the direct line of sight to saidobject through said aperture.

LEO H. BROWN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,454,950 Boyle May 15, 1923669,705 Reeh Mar. 12, 1901 2,045,093 Newcomer June 23, 1936 2,058,484Mihalyi Oct. 27, 1936

